The present invention is directed to an improved radiant energy distribution and detection apparatus for distributing radiant energy about and sensing radiant energy returned or reflected from a target zone, which apparatus is configured to sense the returned or reflected radiant energy substantially at its apparent origin.
While the apparatus of the invention is useful in a broad range of applications, the disclosure will be facilitated by specific reference to use thereof with a device for determining the location of an object within the target zone. (One such device for determining the location of an object within a target zone is disclosed as an "optical touch screen input device" in U.S. Pat. No. 4,553,842, which Patent is assigned to the assignee of the present application.
Two related design problems associated with optically based apparatus or devices are the problems of light losses within the device and the susceptibility of the device to the effects of ambient light present in the operating environment in which the device is employed. Some of the means heretofore employed to decrease susceptibility to ambient light have involved such approaches as filtering of the light employed and installation of baffles or similar devices in the vicinity of the radiant energy detector of the device to interfere with impingement of ambient light upon the detector device. On the other hand, it will be appreciated that the problem of light losses can be aggravated by the installation of additional filtering and baffling devices, each of which will inherently decrease the net radiant energy reaching the detector.
The solutions heretofore employed to these problems generally resulted in additional cost of manufacture of the device and the imposition of additional stringent alignment requirements for various elements of the device to assure proper and accurate operation. Moreover, the scattering of light beams traversing the target zone in some prior art devices often resulted in limiting the resolution of the device.
In our co-pending application, Ser. No. 599,131, filed Apr. 11, 1984, now abandoned, we have proposed an energy distribution and detection apparatus which employs a scanner device configured to both deliver radiant energy to the target zone and to return radiant energy to its point of entry into the target zone after the radiant energy traverses the target zone. The apparatus of our co-pending application uses a radiant energy emission device such as a laser diode which emits a collimated beam of light along a primary beam path in a first direction toward the scanner device or scanning assembly. This scanning assembly sweepingly distributes a discrete beam of radiant energy across the target zone and scans discrete beams of radiant energy returning from that target zone. This apparatus further employs a beam splitter for redirecting radiant energy from the emission device to the scanning assembly and a detector for sensing the presence of radiant energy returning from the scanning assembly.
The beam splitter device is situated within the primary beam path so as to split both the incident beam from the emission device and the incident beam returning from the target zone via the scanning assembly into first and second beam components. The first beam components are substantially continuations of the incident beams in both cases and the second beam components are angularly displaced therefrom. In operation, such a beam splitter device substantially evenly divides the radiant energy contained in the incident beam in each instance between these first and second beam components. Only one of the first and second beam components resulting from the emitted beam is directed to the target zone from the beam splitter. Similarly, the detector device is positioned to receive one of the first and second beam components produced by the beam splitter device in response to the returning beams received from the target zone by way of the scanning assembly. Hence, the detector acts to detect the presence or absence of light for a given orientation of the scanning device relative to the target zone.
It will be appreciated that the above-described use of the beam splitter substantially diminishes the net radiant energy present in the beam incident upon the detector device. That is, the beam splitter effectively halves the net radiant energy both in the beams entering the target zone and in the beams returning from the target zone by way of the scanning assembly. Thus, a maximum of only 25% of the light initially produced by the emission means is available for detection at the detector means. However, the foregoing arrangement greatly enhances resolution by the use of the above-described scanning assembly, as well as by the use of additional structures more fully described in the above-referenced co-pending application Ser. No. 599,131, now abandoned.